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I didn't have any differential problems or noises that I know of in my '98 BMW 323is, but at 137,000 miles and not changed for at least 100k miles I figured I'd do this and the manual trans fluid. I'll review the trans fluid there (Royal Purple Synchromax) since that made a huge difference. My car runs much quieter and smoother after the fluid changes. I can not really tell if this oil made a difference in the differential since I did several changes at once but it definitely didn't make things worse. The old differential oil came out completely clear and was as much fluid as expected so I'm pretty sure things have been running as expected back there.
After I had already ordered this I found that some BMW owners run Mobil 1 gear oil in the differential since it is said to run cooler there than RP or Redline oil. So I could have saved several dollars per quart and maybe gotten better performance, but I don't drive the car hard so this will do just fine. 5 stars since my car is running so much better that I'll give some credit to this oil.
Update 06/2012 Several tanks of gas later and my MPG is higher. Since I replaced the trans fluid and this at the same time, not sure which or if both made the difference. Really improved the highway MPG, and it just did 32.09 MPG, doing the relatively flat round trip Los Angeles to Palm Springs plus some other mainly highway driving. My car has been getting 23 to 24 for the last two years and maybe 25 to 26 before that. I've only hit 32 mpg once before in August 2009, and have had only 6 tanks of gas get over 30 mpg in the almost 12 years I've owned the car. Stop and go driving is just slightly higher than before though as the prior three tanks of gas were 23.03 mpg, 27.38 mpg, 24.99 mpg.
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Recently replaced all the oil in my front dif/rear diff/ and transfer case on an 07 Tundra. Went from Mobile1 to this, and noticed a slight improvement in noise.
I'd use this again.
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I purchased this product to change the differential fluid in my 1970 International Scout. It contains the additive required for the limited slip differential, so that is a bonus.
Sure, there are cheaper oils you can buy for a differential. But from what I have been reading, this stuff is very good and will last much longer than regular "dinosaur" (non-synthetic oil) and will flow at lower temperatures.
I have only done one of the two diff's so far, the rear one, but there already seems to be a slight bit more "grunt" to my tired Scout (an engine rebuild is in the works). I also live in Minnesota, and found my manual transmission, transfer case, and both differentials very "gooey" when the temperature dips down to below freezing. I suspect that this will help somewhat.
On another note, I drained and replaced the fluid in my trans/transfer case with a Castrol "full-synthetic" 5w-50 motor oil, and wow what a difference there! Easier shifts, and much quieter than before. Many think you need to put in a heavy weight oil in these on a truck, but actually many use 50 weight motor oil or standard ATF in their manual transmissions now.
Honest reviews on Royal Purple 05300 Max Gear 75W-90 High Performance Synthetic
I could tell the difference it made in my limited slip differential . It was quieter and seemed smother . to soon to tell if it made a difference in mileage . Yes I would recommend it to a friend .
Paul
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I use this as my gun oil in my Colt 6920 AR as well. Great stuff. Never had any issues with my rear end gears or rifle! Awesome company.
